This method is for determining combined nitrogen in liquefied petroleum gas (LPG). The method determines all nitrogen compounds that are extractable by aqueous acid, including ammonia, amines, nitriles and amides. The method is particularly useful for LPG samples containing nitrogen species, such as ammonia and amines, which can readily adsorb on stainless steel surfaces in contact with the LPG. The procedure yields quantitative results in the range of approximately 0.1 mass-ppm to approximately 3 mass-%.